Abstract: An anchoring device for screws having a casing in the form of a slitted expansion dowel, and an associated expansion body. The casing and the body are connected by a rupturable bridge which can be ruptured by axial movement of the body. The body has suitable elements, embodied as wedge tabs, which engages the slits of the casing. The casing and the body are made of synthetic material. The expansion body has elements which are moved radially outward, and preferably spread, as a result of form-fitting cooperation with countersurfaces located on the casing when the body approaches thereto.